Time tested - many 1000's of these units have been sold and are currently in use. Brand - "The Skylight Guy" - Not all replacement skylights are the same. These Canadian made skylights are the only aftermarket skylights designed with the assistance of the original Westfalia engineer. Every aspect of the original skylight was the result of careful engineering. Of course a proper fit was important, but the exact thickness and composition of the material was just as crucial. The material had to be strong yet pliable, because it was actually engineered to flex. In the event of any impact (from inside or outside the camper), it is supposed to bend slightly and absorb the impact, rather than either crack or (worse yet!) transfer the force of the impact to the hinge points on the poptop and crack the poptop. Only the original German skylight and The Skylight Guy aftermarket skylights adhere to these original specifications. If you look at other aftermarket skylights, they're thicker and more brittle. They don't fit as well with the stock hardware, they don't seal as well, and in the event of impact they are more likely to be damaged or even damage your poptop.
There is one difference between aftermarket and original skylights. All aftermarket skylights - these included - are single-pane in the center instead of double-pane. Only the original is double-pane. The elimination of the additional insulation layer allows the skylights to be as affordable as they are. Note - with any skylight, overtightening will crack the light so please tighten with care.